Diodes Explained - The basics how diodes work working principle pn junction

Hey guys, this is Paul from Engineering mindset.com. In this video we will look at

diodes

to understand the

basics

of how they

work

, as well as where and why we use them. What is a diode? A diode looks like this and comes in different sizes. They usually have a black cylindrical body like a stripe on one end, as well as some wires coming out to allow us to connect it to a circuit. This end is known as the anode and this end is the cathode. But let's see what. that means later in this video you can also get other shapes like the Zener diode or an LED which is a light emitting diode but we won't cover them in this video, a diode allows current to flow in only one direction in a circuit if we imagine a water pipe or the swing valve installed while the water flows through the pipe it will push the swing gate to open it and it will continue to flow.

However, if the water changes direction, it will push the gate closed and prevent this. Therefore, water can only flow in one direction. This is very similar to a diode. We use them to control the direction of current in a circuit. Now we have animated this video using electron flow, which is where electrons flow from negative to negative. positive However, you may be used to seeing conventional flow, which is traditional in electronic engineering and this is where electrons flow from positive to negative. The flow of electrons is what is really happening. But you may still run into the mainstream, as these explanations are easier to understand.

Understand, just keep in mind which one we are using. So if we connect a diode to a simple LED circuit like this, we will see that the LED will only light up when the diode is installed in the correct way and that is because it allows current to flow in only one direction, depending on which direction the diode is installed. This will act as a conductor or insulator For the diode to act as a conductor The stripe end is connected to the negative and the black end is connected to the positive This allows current to flow, we call it forward biasing.

Flip the diode, it will act as an initiator and current cannot flow and we call this reverse biasing. So how does the diode

work

? As you know, electricity is the flow of free electrons, but in atoms we use copper wires because copper has a lot of free electrons, which makes it very easy to pass electricity. We use rubber to insulate the copper wires to keep us safe because rubber is an insulator, which means its electrons are held very tightly and therefore cannot move between our atoms. If we look at the basic model of an atom for a metallic conductor, we have the nucleus in the center and it is surrounded by several orbitals.

Shells, which contain the electrons. Each shell contains a maximum number of electrons. An electron must have a certain amount of energy to be accepted into each shell. Electrons located furthest east, away from the nucleus, contain the most energy. The outermost shell is known as the Valence Shell and a conductor has between 1 and 3 electrons in its valence shell. The electrons are held in place by the nucleus, but there is another layer known as the conduction band. If an electron can reach this shell, then it can break free from the atom and move. to another With methyl atoms such as copper, the conduction band and the valence shell overlap.

So it is very easy for the electron to move. The outermost layer is packed with an insulator. There is little or no room for an electron to bind. The nucleus has a strong control over the electrons and the conduction band is very far away. So electrons cannot reach this to escape, therefore electricity cannot flow through this material. However, there is another material known as a semiconductor. Silicon is an example of a semiconductor with this material. There are too many electrons in the outermost shell for it to be a conductor, so it acts as an insulator. But since the conduction band is quite close, if we provide some external energy, some electrons will gain enough energy to jump from the valence to the conduction band to become free.

Therefore, this material can access both an insulator and a conductor if its silicon has almost no free electrons. So what engineers do is dope silicon with a small amount of another material to change the electrical properties? We call this p-type and n-type doping. We combine these materials to form the diode, so inside the diode we have the two wires, the anode and the cathode, which connect to some thin plates and then in between these plates there is a layer of p-doped silicon on the side of the anode and the n-type cone layer on the cathode side Everything is encased in a resin to insulate and protect the materials Let's imagine that the material has not been doped yet.

So inside there is pure silicon. Each silicon atom is surrounded by four of our silicon atoms. Each atom needs eight electrons in its valence shell. But silicon atoms only have four electrons in their valence shell. So they sneakily share one electron with their neighboring atom to get their eight They want this is known as covalent bonding when we add the n-type material like phosphorus. It will take the position of some of the silicon atoms. The phosphorus atom has five electrons in its valence shell. Just as silicon atoms are shared. electrons to obtain the desired eight. They don't need this extra.

So now there are extra electrons in the material and therefore they can move freely. With p-type doping we add a material such as aluminum or aluminum. This atom has only three electrons in its valence shell, so it cannot provide its four neighbors with an electron to share. Then one of them will have to leave, thus creating a hole where an electron can sit and occupy. So now we have two pieces of Doak silicon, one with too many electrons and one We don't have enough electrons. The two materials join together to form a PN

junction

at this

junction

.

In this region it is known as the depletion region. Some of the leftover electrons on the n-type side will move to fill the holes on the p-side. -type side This migration will form a barrier with an accumulation of electrons and holes on opposite sides. Electrons are negatively charged and therefore holes are considered positively charged. So the accumulation causes a slightly negatively charged region and a slightly positively charged region. creates an electric field and prevents more electrons from moving across the potential difference in this region is about 0.7 volts in typical

diodes

When we connect a voltage source across the diode with the p-type anode connected to the positive and to the n type cathode connected to the negative This will create a forward bias and allow current to flow.

The voltage source must be greater than the 0.7 volt barrier. Otherwise, the electrons cannot make the jump. When we reverse the power supply, then the positive is connected to the n-type cathode and the negative is connected to the p-type anode. The holes are attracted to the negative and the electrons are attracted to the positive and this causes the carrier to expand There the diode acts as an insulator to prevent the flow of current Diodes are represented on engineering drawings with symbols like these The strip on the body it is indicated with a vertical line on the symbol and arrowheads in the direction of conventional current When we look at how a diode We see these numbers and letters on the body that identify the diodes so you can find the technical details online The diode will have an IV diagram that looks like this This diagram plots the The current and voltage characteristics form this curved line.

This side is how it should function when acting as a driver and this side when acting as a motor. You can see that the diode can only act as an insulator up to a certain voltage difference. through him. If it exceeds this it will become a conductor and allow current to flow. This will destroy the diode and probably its circuit. Therefore, you must ensure that the diode is the correct size for the application. Likewise, ground can only handle a certain voltage or current in forward bias. The value is different for each node. And you will need to search this data to find the details.

The diode requires a certain level of voltage to open and allow current to flow forward biased. If we apply a voltage lower than this, it will not open and allow current to flow. But as we increase beyond that, the amount of current that can float will increase. increase rapidly Diodes will also provide a voltage drop in the circuit. For example, when they added this diode to the simple board mounted LED circuit, I get a voltage drop reading of 0.7 1 volts. So why do we use them like? We mentioned that we use diodes to control the direction of current flow in the circuit.

That's useful, for example, to protect our circuit if the power supply was connected backwards. The diode can block the current and keep our components safe. We can also use them to convert alternating current. current into direct current, as you may know, AC or alternating current moves electrons back and forth creating a sine wave with a positive and negative half. But DC or direct current moves electrons in only one direction, giving us a flat line in the positive region if we connect the primary side of a transformer to an AC supplier? And then connect the secondary side to a single diode.

The diode would only allow half the wave to pass and block the current on the opposite side. So the secondary side of the circuit experiences only the positive half of the cycle. So now it is a very approximate DC Circuit, although the current pulses, but we can improve this way of doing it. That is, if we connect Dov to the secondary site, we create a full wave rectifier, the diodes control which paths for AC current can flow for a long time by blocking or allowing them. pass as We just saw that the diodes allow the positive half of the sine wave to pass But this time the negative half is also allowed to pass Although this has now been reversed to make it a positive half Additionally, this gives us a better DC supply because The pulsation has been reduced considerably, but we can still improve this further.

We simply add some capacitors to smooth out the ripple and eventually achieve a smooth line that closely mimics a DC supply. We have covered how capacitors work in great detail in our previous video, check out the links below. So how do we test the diode? So we take our diode and our multimeter? We connect the black probe to the end of the diode with the stripe. Then we connect the red probe to the opposite end. When we do this, we should get a reading on the screen. For example this model one n400 one diode gives us a reading of 0.5 1 6 volts which is the minimum voltage needed to open the diode and allow some current to flow if we now invert the leaves connected to the diode we should see oh L on the display, which means out of limits that is telling us that it is not being able to make a measurement and that is good because it means that it cannot complete the Circuit so the doubt is doing its job if we were to get a reading by connecting in both configurations then the component is defective and should not be used to test the diode in a circuit for voltage drop.

We simply move the multimeter to the DC voltage function and then place the black probe on the striped end and the red probe. At the black end. This will give us a reading of, for example, 0.7 1 volts, which is the voltage drop. Well, that's all for this video, but to keep learning, watch one of the videos on screen now and I'll see you there for the next lesson. , don't forget to follow us on Facebook Instagram Twitter as well as Calm Engineering Mindset